The present invention relates to a method and apparatus for hermetically sealing a semiconductor package, and more particularly to such a method and apparatus in which a semiconductor package having a semiconductor device such as an LSI chip or the like mounted on a ceramic substrate or the like is hermetically sealed with solder being used as a sealing material.
In a semiconductor package having such a high packing density that it is difficult to sufficiently ensure a sealing area by a gasket, a method is advantageous in which a substrate having a semiconductor device mounted thereon and a cap are hermetically sealed by solder bonding. In this sealing method, the prevention of the inflow of a sealing solder into the package and the generation of defects such as pin holes or the like, as well as the control of the amount (or height) and the shape (fillet profile) of the sealing solder, are important in an aspect of the sealing performance.
JP-A-61-276237 has disclosed a method and apparatus in which a semiconductor package is hermetically sealed in a gas pressure controlled chamber in such a manner that in a state in which priming solders (or pre-solders) applied on bonding portions of a substrate and a cap of the semiconductor package are heated and fused by a heater provided in the vicinity of the bonding portions, the substrate and the cap are brought in proximity to each other so that a distance between both the bonding portions becomes smaller than a desired value and the fused solders contact each other, the substrate and the cap are thereafter moved in reverse directions to bring the distance between the bonding portions to the desired value, and the solders at the bonding portions are cooled and solidified by lowering the heater temperature in a state in which the distance between the bonding portions is kept at the desired value. A gas pressure in the chamber is reduced with the progression of cooling so that a balance between a gas pressure in the semiconductor package and the gas pressure in the chamber is held until the solder at the bonding portion is solidified.
JP-A-63-299255 has disclosed a sealing apparatus in which the sealing is performed in a gastight chamber in such a manner that a semiconductor package is placed on a plate-like heating/cooling device and is heated and cooled by the plate-like heating/cooling device to fuse and solidify a sealing material (or solder) with a pressure in the gastight chamber being increased or decreased in accordance with the heating or cooling temperature of the heating/cooling device so that the gas pressures inside and outside the semiconductor package become the same.